CROSS REFERENCE TO RELATED PATENT APPLICATION
Patent application Ser. No. 07/979,121 filed Nov. 20, 1992, now (U.S. Pat. No. 5,371,766) entitled "Clock Extraction and Data Regeneration Logic for Multiple Speed Data Communications," assigned to the assignee of the present invention, in part, describes an apparatus and method for detecting ring speed based upon the histogram of signals recovered from the network.
1. Field of the Invention
The invention relates to communications networks in general and, in particular, to the management of local area networks (LANs).
2. Prior Art
Multi-rate digital communications networks are used as the preferred data highways to distribute information between data terminal equipment, computers, work stations or the like. Local Area Networks (LANs) are one type of multi-rate digital communications networks used to distribute information within limited geographical areas, such as college campuses, buildings or the like.
The token ring LAN is a well-known multi-rate digital network proposed by IEEE 802.5 Standards. Signal transmission on the network is unidirectional and access to the network is provided via a unique data pattern called a token. The network can operate at different speeds, for example, 4 Mbps or 16 Mbps.
Even though a token ring LAN can accommodate devices such as adapters, concentrators, bridges routers or the like operating at 4 Mbps or 16 Mbps, both speeds cannot be accommodated on the same network simultaneously. If this were to happen, network degradation due to data loss, failure to recover the token and other network problems would result.
To avoid the undesirable results, the prior art has adopted mechanisms and techniques for a device to determine the rate at which data is being transmitted on a LAN before the device inserts into the network. The most obvious approach is for a user to know the speed at which the LAN is operating and set the device to enter the network at the predetermined speed. Even though this technique works well for its intended purpose, it tends to be cumbersome, since it requires manual intervention by an operator.
In addition, the device could be set to the wrong speed due to operator's error.
Published European patent application 0425317AZ describes an interface system which detects the speed at which the network is operating by counting the frequency at which data is recovered from the network. Even though this system is a step in the right direction in that it automatically determines the ring speed, one of its drawbacks appears to be its reliability. For example, if no station is connected to the media, the system could measure the harmonics in the media and report a wrong ring speed. In fact this error condition could occur even when other stations are connected to the network.